The present invention relates generally to welding systems and, more particularly, to a wire feeder connected to a constant current (CC) power source and designed to automatically adjust the speed by which consumable welding wire is delivered to a weld so as to maintain a target voltage at the weld.
Wire feeders are typically used to feed metal wire into a weld during a welding process such as Gas Metal Arc Welding (GMAW) and other welding processes. Typical wire feeders have a drive roller assembly for driving the metal feed from a feed spindle through a welding gun for introduction to the weld. Power is supplied to the drive roller assembly by a welding power supply via a weld cable. The amperage or current generated by the power supply governs the speed in which the metal feed is fed to the weld, or the wire feed speed (WFS). Generally, the higher the amperage supplied to the wire feeder, the greater the WFS. Conversely, if voltage is used to govern the WFS, the lower the voltage, the higher the WFS. Accordingly, the speed by which the wire feeder supplies the filler metal to the weld is a direct function of the power delivered to the wire feeder and therefore, the weld. The thickness of the metal being welded determines the power required at the weld and thus the WFS necessary to deliver that power. A thicker metal requires higher power to effectively weld.
Typically, power sources, which may be designed to supply power to the wire feeder, have been constructed to operate in either a constant current (CC) mode or a constant voltage (CV) mode. For those welding applications that require a constant current input to the wire feeder, the wire feeder is connected to a CC power source. Conversely, for those welding applications that require a constant voltage at a weld, the wire feeder is connected to a CV power source. For CC mode of operation, the user is able to adjust the speed by which metal filler or consumable electrode is delivered to a weld so as to maintain a desired voltage at the weld. Conversely, for a CV mode of operation, the user may adjust the wire feed speed to maintain a target current level at the weld. Wire feed speed (WFS) and voltage at the weld are inversely related therefore to increase the arc voltage at the weld, the WFS must be decreased and to lower the voltage at the weld, the WFS must be increased. In contrast, WFS and current are directly related and, as such, an increase in WFS will cause an increase in current and vice versa.
For most GMAW welding applications, it is necessary that the wire feeder be connected to a CV power source. For example, short circuit transfer is a welding application that is characterized by a less than 21 volt arc voltage. With a CV power source, the user is able to set a desired target voltage that may be less than 21 volts and adjust the speed by which wire is delivered to the weld to control output current. Accordingly, the user may increase output current by increasing WFS while the voltage at the weld is held at the target level by the CV power source. In contrast, CC power sources are typically not usable for short circuit transfer applications.
CC power sources are designed to maintain a constant output current level. The user inputs a desired target current level on the power source and the operational circuitry of the power source operates to maintain an output current level. The user may then adjust the WFS to regulate a voltage at the weld. To increase the voltage at the weld, the WFS is decreased. To decrease the voltage, the WFS is increased. If the weld is underpowered, the weld will be insufficient to adequately join the materials being welded. On the other hand, if the weld is overpowered, it is possible to “burn through” the materials being welded. As such, the user must proactively monitor the weld and adjust the WFS accordingly.
Typically, however, the wire feeder will control the WFS within a limited range of values. As a result, when the wire feeder is operating on a CC power source, the user may be unable to get a desired voltage level at the weld. For instance, for short circuit transfer applications, an arc voltage of less than 21 volts is generally required. However, achieving an arc voltage of less than 21 volts may not be possible given the constant current level being maintained by the power source. That is, at the current level selected by the user, additional power may be needed at the weld to sufficiently fuse the materials. To increase the power at the weld, the user will decrement the WFS to increase the arc voltage. Because the wire feeder has a limited range of acceptable WFS values, it may not be possible for the user to decrement the WFS to a level needed to adequately increase the arc voltage. As a result, the weld is underpowered and the materials may not be properly fused. Similarly, to prevent “burn through” the user may seek to increase the WFS to drive the voltage downward to a level that is not permitted by the wire feeder.
Therefore, to carry out a particular short circuit transfer application, a CV power source may be required which increases equipment costs and accentuates the under-utilization of the CC power source. Additionally, multiple power sources increases the costs associated with maintenance as well as storage.
It would therefore be desirable to have a system and method capable of duplicating CV mode of operation with a CC power source.